Classifier for dry impalpable fines



April 12, 193s. R GERHARDT .I 2,113,885

CLASSIFIER FOR DRY IMPALPABLE FINES Filed Dec. 24, 1936 wmwpm y Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE half to William G.

Broadfoot, Wilmington,

Application December 2 4, 1936, Serial No.117,640

4 Claims.

One of the recognized inherent drawbacks in.`

the operation of centrifugal classifiers is that while they do separate the impalpable fines fromA the coarser granules, they are unable to deliver the impalpable fines segregated from the next coarser grade.

vIt will be understood by those skilled in the.

art that' centrifugal force acts to throw the heavier particles outward and as a result of the outward displacement of the heavier particles, the lighter particles remain in the less ldisturbed area toward the center of rotation of the centrifugal mechanism-the portion of the powdered substance which is of impalpable flneness being suspended inthe atmosphere around the axis of rotation, there being no way to get it out so that as it increases in density itis entrained in the flow of larger particles, being carried out,-

ward by centrifugal force, being discharged in mixture with the particles of next coarser grade.

'Regardless of how many grades of material Y the centrifugal classifier is capable of separating,

the fact remains that the finest grade delivered ls a mixture including the impalpable powder or dust which would form a grade 'to itself providing the centrifugal classifier were` able to separate it out.

'I'he object of the present invention is lto remove the impalpable nes from the region adjacent the axis of the centrifugal mechanism of a classifier of this type and to deliver it as agrade separate and distinct from' the grades which the classier is normally able to deliver, this being `accomplished by means which form the subject matter of the following specification and being illustrated in the drawing accompanying and forming a part of the same. y

Other objects of the invention will'appear as the followingA description of a preferred and practical embodiment thereof proceeds. v

"In the drawing which illustrates a practical embodiment vof my invention:

Figure 1 is a vertical section through a lcentrifugalfclassier embodying the features of my invention; and 'f Ythe illustrative mechanismit lmay be stated Ithat there are a number of structurally different cenvFigure 2 is across section vtakenralong the linev trifugaliseparatora any of which-may be employed as an element in my novel combination, the one herein illustrated being of well known construction and selected by reason of 4its simplicity. It comprises an outer casing I having a cylindrical upper portion 2 and a conical lower portion 3. The lower portion has a discharge 4.

Within the cylindrical portion of the outer cas'- ing I is a cylindrical baille 5 of smaller diameter than the outer casing defining an annular chamber 6. Within the conical lower portion 3 of the casing is a cone 1 open at its upper end 8 and having a discharge 9. The baille 5 and cone 1 are spaced apart as at I forming anair entrance which is guarded by an annular series of bars II. The baille is spaced below the -top wall I2 of the outer casing I forming an air space in which works ra'fan I3 mounted on a hollow shaft I4 which extends toa poi-nt outside of the casing I and has a driving gear I5, by means of which the shaft Ill and fan I3 are rotated. The

baille 5 is provided with an inwardly extending.

annular flange I6 beneath the blades of the fan I3, leaving a central opening I1 beneath the central portion of the fan. On the bottom of the rotating shaft I4 a circular distributing device I8 is positioned, said distributing device compris ing spaced plates I9 and 20. A fixed tube 2i extends through the hollow` shaft I4 and'discharges on to the plate 20. At the upper end of the fixed tube 2| is a funnel 22.= Material to be classified is poured in through the funnel 22,4

lands on the rotating plate 20 from which it is of the air current from thepressure side of the fan `divides and passes` downward through` the space between the cone and the conical portion of thev outer casing. That part Vof the material thrown outwardly by theplate 2|), and which` does, not immediately gravitate down into the cone I isintersected land entrained vb'v the upwardly flowing current `and vvcarriedinto"the path ofthefan where it is thrown` outwardly intojthe f rannular' chamber Bfand'travels downfthe space y between the cone and lower yportion ofthe outerv casing ina vehicleof-moving air y, ar1'd 'i s finally discharged at the point 5.

It will be understood that lconventional structure isnow being described in which the revolving gate 24 is not present so that the discharge 4 is freely open. The displacement of air ladened with the heavier solid matter in an outward direction through centrifugal force by the fan I3 causes a contra-displacement of the air laden with the impalpable dust in an inward direction,

the dust remaining in suspension in what may be termed an inert core of air occupying the central part of the baffle 5 and bounded on the outside by the upward air ilow from the bottom of the baiile 5 to the fan. In conventional structure there is no means for removing this suspension as a segregate entity so that as it becomes added to from the top by the action of the fan, it is dissipated laterally by being entrained inthe upwardly directed air currents and passes outwardly through the fan down through the chamber 6 and through the space between the cone and the lower portion 3 of the outer casing, being impelled by that part of the air current which flows through the space between the cone and the lower portion of the outer casing.

It is the object of the present invention continually to withdraw this central suspension of impalpable nes. With this end in view provision is made for rarefying the air in the central region of suspension. This reduces the particlesupporting capacity of the air and the larger particles of suspended matter gravitate downward into the cone 1. Means are provided for creating an upward air ow to draw the suspended matter out of the apparatus without permitting it to become mixed with any of the grades of less flneness. Such means comprises in the present illustrated embodiment of the invention,

Va hood 25 positioned on top of the outer casing I and having an inverted mouth 26 of considerable width so that it will promote an upward drift of the suspension atmosphere rather than a jet of the same. The mouth is defined by a downwardly projecting ange -21 extending as close as practicable to the fan I3. The hood is in communication by way of a conduit 28 with an exhaust fan chamber 29 housing a suitable exhaust fan 30 which sucks from the hood and delivers to a cyclone collector or other similar apparatus not shown.

Within the hood the shaft I4 is provided with blades 3| pitched in a direction and at such an angle as to cause the upward drift of the suspended matter referred to. The hood is preferably bevelled at the top as shown at 32 bringing the wall of the hood close to the path of the blades 3| avoiding inert pockets of dust-laden air and facilitating the displacement by the blades 3l of suspended matter rising on the side of the hood remote from the conduit 28.

With the end 1n view of collecting all of the impalpable suspended matter, it is desirable that no portion of the air current owing downwardly through the annular chamber 6 should be diverted into the space between the cone 1 and the lower portion 3 of the outer casing I, for as has been stated,such air current carries with it som e of the impalpable matter in addition to the fines which are ordinarily delivered through the discharge 4. In order to prevent this diversion of a part of said air current, the gate 24 is provided, which comprises a casing 33 having an opening ln one end registrable with the discharge 4 and an outlet opening 34. A driven shaft 35 rotates at a predetermined speed within said casing carrying vanes 36, the outer ends of which revolve in substantial engagement with a cylindrical intermediate part of the casing 33. The blades 36 are so spaced that in any position of the shaft 35 they block the passage of an air current through the discharge 4. The nes which the discharge 4 is designed to deliver fall by gravity into the pockets between the blades as said pockets are successively 'presented to the discharge 4 and by the rotation of the pockets they are dumped through the outlet 34. of the blocking of air flow through the discharge 4, a body of inert air remains in the space between the cone 1 and the lower portion 3 of the outer casing. This means that the entire current after having dropped the ncoarser nes at the point where its velocity is checked against the bars II, returns upwardly within the cylindrical baiile 5 carrying all of the impalpable nes y which by the contra-displacement produced by the centrifugal action of the fan I3 pass into the central inert region of the classifier where they are drawn upwardly in the manner already described and taken out by the exhaust fan 30.

The discharge 9 is also preferably controlled by means of a similar gate 31 having vanes 38 blocking the passage of air currents through the discharge 9 preventing the diversion of any part of the nes-laden current through said discharge. 'I'he gates 24 and 31 may be speed controlled.

It will of coursel be understood that the pull of the blades 3I rarees the air in the central portion of the classifier so that it is no longer able to support the heavier particles in the sus`- pended matter which particlesdescend by gravity into the cone 1 and out by way of the discharge 9 so that only the finest powder is withdrawn by the exhaust fan 30. The degree of neness of the impalpable fines may be regulated by varying the -speed of the exhaust fan 30. When the exhaust fan is speeded up, the suction in the central region of the classifier is increased thereby robbing the lateral upwardly flowing current of more or less of the grosser particles which it is carrying.

While I have in the above description dened what AI believe to be a preferred and practical embodiment of my invention, it will be understood to those skilled in the art that the details of construction as illustrated and described are merely by way of example and not to be construed aslimiting the vscope of the appended claims.

WhatY I claim is:

1. Classiiier for dry comminuted substance comprising a casing, means within said casing defining therewith inner and louter chambers. the inner Vchamber communicating both above and below with the outer chamber, a centrifugal fan creating a circuitous air current up through the inner chamber and down through the outer chamber, a centrifugal distributor in the lower part ofthe inner chamber obstructing the centra] part of said chamber, thereby diverting the said air current, making it flow close to the wall of said inner chamber and leaving the atmosphere in the central part of said inner chamber above said obstructing means inert, means for feeding ungraded material on to said distributor whereby it is spread centrifugally in said air current, means providing separate paths of exit for tailings and intermediate fines, the tailings dropping by gravity into one path, the fines being carried by said current into the path of said fan, the latter member throwing out the heavier granules in the other path of exit, the substantially In viewv impalpable particles by contra-centrifugal dis- 75 atrasos placement being moved into the inert central part of the inner chamber, means for simultaneously rarefying the atmosphere in said central part, causing the gravitational drop of the heavier particles of suspended matter, and drawing the remaining suspended impalpable fines out through an independent exit.

2. Classier for dry comminuted substance comprising a casing having an upper separating portion and a lower receiving portion, an annular open ended baiile within said upper portion deiining with the adjacent part of said casing inner and outer chambers, a receiving member for tailings below and spaced from the lower end of said bailie, and spaced from the receiving portion of said casing forming a passage for intermediate iines, said receiving chamber and passage having independent outlets, said inner4 chamber communicating both above and below said baiiie with the outer chamber, a centrifugal fan creating a circuitous air current up through the inner chamber and down through the outer chamber, a centrifugal distributor in the lower part of the inner chamber obstructing the central part of said chamber thereby diverting the said air current, making it flow close to the Wall of said inner chamber and leaving the atmosphere in the central part of said inner chamber above said obstructing means inert, means for feeding ungraded material on to said distributor whereby it is spread centrifugally in said air current, the tailings dropping by gravity into said receiving member and the intermediate iines being car- -ried by said current into the path of said fan, the

pendent exit, and a gate controlling the discharge of intermediate fines from said passage while inhibiting unrestricted air flow through said passage, diversion of any substantial part 6i said air current through said passage being thus inhibited or controlled. e

3. Classiier for dry comminuted substance comprising a casing, ai annular baiilewithin said casing dening therewith inner and outer chambers, the inner chamber communicating both above and below with the outer chamber, a cen'- trifugal fan creating a circuitous annular air current up through the inner chamber and down through the outer chamber, a centrifugal distributor in the lower part of the inner chamber obstructing the central part of said chamber, thereby diverting the said air current making itf flow close to the wall of said inner chamber and leaving the atmosphere in the central part of said inner chamber above said obstructing means inert, means for feeding ungraded material on to said distributor whereby it is spread centrifugally in said air current, means providing separate paths of exit for tailings and intermediate iines,

the tailings dropping by gravity into one path,

the nes being carried by said current into the path of said fan, the latter member throwing out the heavier granules into the other path of exit, tho substantially impalpable particles by contracentrifugal displacement being moved into the inert central part of the inner chamber, means forming a dome above said casing and in com--A munication with said central part of the inner chamber, a conduit communicating with said' dome providing a discharge separate from the aforementioned paths of exit, a suction fan in said conduit, and means in said dome for rarefying the atmosphere in the central part of said inner chamber and for drawing the suspended matter upward into said dome and toward the mouth of said conduit.

4. Classier as claimed in claim 3, said rarefying means including pitched blades rotatable unitarily with said` centrifugal distributor.

PAUL GERHARDT. 

